我无法安装 Vim，需要帮助。我尝试了以下方法：
root@cbitlab1:/home/cbitlib1# sudo -s
root@cbitlab1:/home/cbitlib1# apt-get install vim
Reading package lists… Done
Building dependency tree
Reading state information… Done
Package vim is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package ‘vim’ has no installation candidate
我该如何解决这个问题 - 我在 14.04。